Process of and product for photographic etching



Patented Mar. 25, 1930 UNITED STATES PATENT OFFICE ALEX BROOKING DAVIS,OF CINCINNATI, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO KEYSTONE WATCH CASE CORPORATION,

PORATION OF PENNSYLVANIA OF RIVERSIDE, NEW JERSEY, A COR- PROCESS OF ANDPRODUCT FOR PHOTOGRAPEIC ETCHING No Drawing.

This invention relates to novel improvements in the art of photography,and it has particularly to do with a photographic film which has specialadvantages when used .in the process of etching. The invention alsopertains to a novel process of preparing the film and to the process ofusing and treating the film when employed, for instance, in etching andsimilar Work.

The detailed description of the invention and its application and usewill herein be made as bearing on the art of etching, al-

though it is to be understood that the invention is not limited thereto.In this art of etching it is well understood the light sensitive film isknown as a resist.

Various processes for transferring a light pattern upon a resist,developing the pattern in the resist by washing out that portion of theresist rendered insolubleby the light and etching the surface thusprepared, have been described and patented. There is also considerablesuggestive and descriptive matter concerning these processes in variousarticles which have been published in the scientific journals. Of allthe light sensitive substances which have been used, probably the mostattention has been devoted to asphalt, and yet asphalt has proven todate one of the least satisfactory substances. I

V. Valenta of Vienna, Austria, in Photographische Korrespondenz, 1910,describes a process for using asphalt, in which he claims to haveeliminated many of the difficulties previously encountered, and hisprocess is for treating asphalt with sulphur chloride, therebyconverting it into a series of resins, among which he recognizes oneparticular substance called gamma-resin as being the most highly lightsensitive.

Other researchers in this art have given attention to asphalt, and toasphalt compounded With certain sensitizers, but the results of theirwork 'give products which are unstable after one day and, therefore,unsatisfactory for commercial use. i

' As a result of numerous researches carried on by me as improvements inthe Valenta process, I have found that asphalt may be converted bycarbon bisulphide and sulfur Application filed December 16, 1926. SerialNo. 155,336.

chloride into a resist for photo etching, which resist is not onlysuper-sensitive but which is perfectly practical after it has beencompletely prepared and stored for more than sixty days. I have,therefore, from my experiments prepared a photo etching resist which isstable over a long period of timeand which has shown no sign ofdeterioration. Thus, I have developed an asphaltic resist which, due toits stability over a long period of time, makes it particularlyadaptable and advantageous for commercial use. It is to be understoodthat a resist adaptable for commercial use must be one which may besatisfactorily shipped from place to place, or that may be manufacturedand held in reserve for a long period of time for factory practice.

While the term asphalt has been herein used without qualification, it isto be noted that Valenta calls for a Syrian asphalt for his use. Byreason of my improvements I find that I may use any asphalt or aprepared or treated asphalt. Thus, my improvements permit a much moreefliciently prepared resist, and a resist which has a much wider usewhile at all times it is particularly adaptable for commercial use. Inaddition to pre paring a satisfactory commercial resist from practicallyany grade of asphalt, I have found that my improvements permit me tosubstitute the asphalt by various other resins and hydrocarbons. f 1

For the purposes of definiteness and of scientific uniformity, I preferto consider the asphalt, its equivalents and substitutes as beinghydrophobic colloids, which term is considered to refer to substanceswith colloidal properties, insoluble in water but soluble in an organicsolvent. Valentas asphalt and resins are to be considered as beingwithin and of such clearness that they may all be readily understood andconsidered.

The numerous writers on asphalt ,have emphasized the desirability ofusing Syrian asphalt as the raw material, it apparently containing thegreater proportion of light sensitive ingredients. I have found thatthis is not necessarily true, for by carrying out the Valenta processwith the new and additional detail which is the basic discovery of thisinvention, practically any kind of asphalt available in the market maybe used, and, I have made highly satisfactory resists from ordinaryTrinidad and Mexican asphalts, which resists are stable over longperiods of time and which are so sensitive that they need only anexposure of 15 seconds when used with asuitable arc and condenser withan interposed light pattern carried by a glass screen.

The detail which has been added by me to the Valenta process to obtainthese results will be evident when it is considered that in the Valentaprocess 25 grams of Syrian asphalt is dissolved in 150 cc. of carbonbisulphide to which is gradually added 2 gms. of sulfur chloridedissolved in 8 cc. of carbon bisulphide. The excess of carbon bisulphideis then distilled OE and the resulting product dissolved in benzol asthe solvent, and oil of lavender as the sensitizer added, and theexposed film resulting from the use of this solution being developedwith turpentine. In my process, using ordinary Mexican 'as-- phalt, thesulfur chloride solution is added to the asphalt solution all at once.Practically all of the carbon bisulphide is removed by distillationafter the re-action is complete, and the resulting mass dissolved inbenzol. I have found that turpentine is excessively active, and insteadof the pure substance, I prefer to use it in ,a modified form with itssolvent power reduced, by the addition of a portion of petroleumbenzine.

Plates of metal or other surfaces to be etched when coated with theresist thus prepared and upon which the resist is deposited in the formof a thin film, are now dipped in ether for 15- seconds before exposureto light, the ether in this short time removing from the coating thoseportions of the resist which are undesirable and which, if left in thefilm, tend to cause the film to wash away too readily after exposure bythe developing solution. I have found this process of dipping the coatedplate in ether for 15 seconds a further advantage in that it distinctlyhardens up the film and leaves it in a condition to adhere to the metalsurface very firmly. The plate after exposure is again dipped in ether,and after develo ment to the desired degree in a mixture of 5%turpentine and 25% petroleum 'benzine, is then dipped in pure pe--troleumbenzine, which has the eflect of instantly stoppingthe furthersolvent action of the turpentine uponthe resist so that the degree ofdevelopment may be stopped-at any time desired by the operator. The thusprepared plate is now baked and etched.

In carrying out my process in detail, I proceed as follows: 25 gms. ofasphalt of any of the softer commercial grades available in the market,are dissolved in 150 cc. of carbon bisulphide at room temperature, andinto this solution, there is immediately poured a solution of 2 grams ofsulfur chloride dissolved in 8 cc. of carbon bisulphide. The mass is nowwarmed on the water bath until the main reaction resulting probablyinthe simultaneous sulfurization and chlorination of the more sensitiveasphalt ingredients, has proceeded to completion, when all of the carbonbisulphide which can be readily removed at water bath temperature isdistilled off. The resulting residue is now'dissolved in 150 cc. benzol,the solution filtered from a small amount of insoluble matter and thissolution is immediately ready for use when 2% oil of lavender is addedas an accelerator and sensitizer.

From the above description, it is evident that my solution of resist ismuch more concentrated than that used by Valenta, who dissolved the sameamount of materials in 500 cc. of benzol at the end, and I thereforeobtain heavier films which are much more resistant to the action of theetching bath.

While the sulfur chloride which has been 1 added to the asphalt solutionhas been mainly or wholly decomposed during the re-action, it isevident, nevertheless, that since it is capable of liberating bothchlorine in the free state and hydrochloric acid as theresult of itsac-' tion with asphalt, and also of free sulfur, any or all of thesesubstances, as well as their products of combination may not only act aslight sensitive films proper, but certain of the resulting compoundsundoubtedly act as accelerators and sensitizers therefor, since oil oflavender alone, without these substances,

possesses no such powerful accelerating effect.

The application of the resist as above prepared is applied to thedesired surface in any known manner, and where the articles are small,preferably on a whirling table, where the volatile benzol solventimmediately evaporates. The resulting film is then dipped in ether,exposed, again dipped in ether and developed as abovedescribed. Afterthe development, the article bearing the picture so obtained is heatedon a hot plate to drive out the last portion of solvent and at the sametime to in some measure sinter the film to get maximum adherence to thesurface, so that at no point will it be moved from the surface by theaction of the electrolyte in an electrical etching bath.

While this process as above described is particularly applicable to theproduction of designs by means of etching, it is evident that eitherbefore or after etching, designs may be plated thru the resist by wellknown electroplating processes, and it then becomes possible to depositthe design'in a metal of one color upon a metal of an entirely differentcolor, and if the metal be first etched and subsequently plated, thesurface may be left smooth, while if plated without etching, the designthen appears as a superimposed or raised surface.

The main differences herein over the Valenta process as shown by theabove description are that any ordinary soft asphalt which I have triedcan be used; the sulfur chloride is added all at once and this resultsin the reaction taking a course apparently quite different from thatwhen it is added slowly; practically all the carbon bisulphide isremoved before dissolving in benzol; the amount of benzol used isdecreased materially, resulting in a more concentrated resist solution;and means are provided for modifying the activity of the turpentine as adeveloper by reducing its solvent power by the addition of petroleumbenzine. The use of ether after the application of the resist is anadded detail of importance which is particularly advantageous to theprocess in that it purifies for photographic purposes the resist in theform of its film directly upon the surface, by its selective solventaction renders the development more accurate and uniform and in somemeasure increases the light sensitivity.

Inasmuch as I have found that practically any asphalt may be used, itappears that many other resins and hydrocarbons in general may beapplicable to this process, for I have already obtained pictures inwhich this process was carried out as described except that ordinarypine rosin was used in place of asphalt, and this process, therefore,evidently has the power of converting other substances than asphalt intolight sensitive films capable of being used in the etching art. Neitherdo I restrict this invention to the use of ether, commonly understood tobe ethyl ether, as the only solvent which might be applicable to bringabout the effects described,

for I know that methyl ethyl ether and certain other solvents of anethereal character are suitable substances to be used in place ofordinary ethyl ether, and in fact, I construe any organic solventcapable of removing the undesirable portion of the treated hydrophobiccolloid from the light sensitive film as falling within the scope ofthis invention.

It is to be understood that the fore oing description of the improvedresist an the process of use thereof may be varied to some extent, butsuch variations and changes as may be desired are considered as beingwithinthe scope of the invention as would be permitted by the broadinterpretation of the following claims.

What I claim is 1. A photographic 'etching prepared by coating theobject to be etched with a solution of asphalt, allowing the solvent toevaporate, washing the deposited film with ether, exposing to a lightpattern, developing the image and etching.

2. A photographic etching prepared by coating the object to be etchedwith an artificially treated asphalt, washing in a suitable medium toincrease the sensitivity of the asphalt to light, exposing'to a lightpattern, developin and etching.

8. A p otographic etching prepared by coating the object to be etchedwith an artiexposing to a light pattern, etching.

4. A photographic etching prepared by coating the object to be etchedwith sulfurized asphalt, washing with a suitable medium to increase thesensitivity of the coating to light, exposing to a light pattern,developing and etching.

5. A photographic etching prepared by coating the object to be etchedwith sulfurized asphalt, washing with ether, exposing to a lightpattern, developingand etching.

6. A photographic etching prepared by coating the object to be etchedwith a solution of sulfurized asphalt, allowing the solvent toevaporate, washing with ether, exposing to a lightpattern, developing,baking and etching.

7. A photographic etching prepared by coating the object to be etchedwith asphalt combined with sulfur chloride, washing with ether, exposingto a light pattern, developing and etching. 1

8. A photographic etching prepared by coating the object to be etchedwith asphalt combined with sulfur chloride and oil of lavender, washingthe coating with ether, ex posing to a light pattern, developing andetching.

9. As a resist for photographic etching, the benzol solution of theproduct of the reaction between asphalt in solution in an organicsolvent and approximately 8% of its weight of sulfur chloride added tothe asphalt solution all at once.

10. A supersensitive asphaltic resist for photo etching capable ofresisting the action of the electrolyte in an electrical etching bathfor at least. thirty minutes and of being rendered insoluble by exposureto a light pattern projected thereon by means of an arc and condenserwithin one minute, produced developing and by the reaction between asolution of asphalt processes.

rocess said rint bein an ima e vunder the for photographic purposes,

12. A photographic medium adapted to receive-a design therein byexposure to light, said medium being a thin layer placed on the objectto betreated and having been subjected to the action of ether for afraction of a minute before being subjected to light.

13. A photographic medium adapted to receive a design therein byexposure to light, said medium being a thin layer placed on the objectto be treated and havingbeen subjected to the action of ether forpossibly fifteen seconds before being subjected to light.

14. A print "produced by photographic formed underthe selective actionof light in a com position including therein sulfurized asphalt andhaving been treated with ether before exposure.

15. A print produced by photographic rocess, said print being an imageformed nder the selective action of light in a composition of sulfurizedasphalt governed by carbon bisulphide, sulfur chloride and a solvent.

- 16. A print produced by photographic process, said print being animage formed selective action of light in a composition of sulfurizedasphalt governed by carbon bisulphide,

17. In the process of preparing a photographic resist having sulfurchloride therein, the step of adding at one time to a hydrophobiccolloid the entire required amount of sulfur chloride; 1

18. In the process of preparing a resist including the reaction productsof a hydrophobic colloid, sulphur chloride and carbon disulphide forphotographic purposes, the step of dipping'the resist after being placedon an object in a solvent of ethereal character before exposure.

19. In the process of preparing a resist the step of dipping the resistafter being placed on an object in ether before exposure.

20. In the process of etching, the step of dipping the resist afterbeing placed on an object in a solvent of ethereal character afterexposure to light projected through a pattern. 21. In the process ofetching, the step of dipping the resist including the reaction productsof a hydrophobic colloid, sulphur chloride and carbon disulphide afterbeing sulfur chloride and benride and carbon disulphide on an object tobe etched and dipping the resist 1n a solution of ethereal characterbefore exposure to light and again after exposure.

23. In the process of etching, the steps of placing a resist includingthe reaction products of a hydrophobic colloid, sulphur chloride andcarbon disulphide on an object to be etched, and dipping the resist'inether before exposure to light and again after exposure.

24. The process of preparing a resist for photographic purposes, whichprocessconsists in adding the total required amount of sulfur chlorideto a hydrophobic colloidacting as a base, adding carbon bisulphide,heating to remove a material amount of said carbon bisulphide, anddissolvingthe resulting mass in a suitable solvent.

25. The process of preparing a resist for photographic purposes, whichprocess consists in adding carbon bisulphide to asphalt, adding at onceall of the requirements of sulfur chloride, distilling substantially allof the carbon bisulphide from the mixture, and dissolving. the resultingmass in benzol.

26. In the process of etching,

the steps of I phide to a hydrophobic colloid, adding sulur of saidcarbon bisulphide, and dissolving the resulting mass in benzol; coatingan article to be etchedwith the resist as formed, dipping the resist 'inether before exposure to light, dipping the resist after exposurein asolvent of ethereal character, developing the image formed in saidresist, and etching.

2,7. In the process of etching the steps of providing a resist by addingcarbon bisulphide to a hydrophobic colloid, adding sulfur chloride,heating to distill a material part of said carbon bisulphide, anddissolving the resulting mass in benzol, coating an article to be etchedwith the .resist as formed, dipping the resist in ether before exposureto light, dipping the resistafter exposure in a solvent of etherealcharacter, developing, dipping the resist in a solution for arrestingthe developing action, and etching.

28. -In the process of etching, the steps of providing a resist byadding carbon bisulphide to a hydrophobic colloid, adding sulfurchloride, heating to distill a material part of said carbon bisulphide,and dissolving the resulting mass in-benzol; coating an article to beetched with the resist as formed, dipping the resist in ether beforeexposure to light, dipping the resist after exposure in a solvent ofethereal character, developing in chloride, heating to distill amaterial part turpentine, dipping in petroleum benzine to arrestdeveloping action, and etching.

29. The process of etching which consists in forming a resist by addingcarbon'bisulphide to asphalt, adding thereto the full requirement at onetime of sulfur chloride, heating the resulting mass to remove a material amount of the carbon bisulphide, dissolving the resulting mass inbenzol; applying the resist as formed to an article to be etched;dipping said resist as applied in ether for a friction of a minutebefore exposure to light, exposing the resist to a design-interceptedlight; dipping the resist after exposure in ether, developing the resistin a mixture of turpentine and petroleum benzine; then dipping theresist in pure petroleum benzine to arrest the developing action; bakingthe resist to cause the-same to adhere firmly to the object; and etchingin a suitable solution.

30. The process of etching corrodible sur-- faces by coacting them witha hydrophobic colloid bearing constitutionally combined sulfur andchloride, removing from the film coating undesirable constituents bywashing with a suitable solvent, exposing the resulting purified film toa light pattern, developing, and etching the resulting picture.

31. The process of photo etching consisting of applying to a corrodiblesurface a resist including the product of the reaction between asphaltand approximately 8% of its weight of sulfur chloride added thereto allat once, dissolved in carbon bisulphide as the mutual solvent and fromwhich all excess carbon bisulphide has been removed at water bathtemperature and the residue dissolved in benzol; exposing the resultingfilm to a light pattern, developing the pattern by 40 means of asolution including turpentine, baking the resulting coated surface, andetchmg.

32. A photographic resist, including the reaction product of ahydrophobic colloid,

sulphur and chlorine, and a suitable sensitizing agent, said sensitizinagent being applied to the product resulting from the comination of thecolloid, sulphur and chlorine, whereby to enhance its light sensitivity.

33. A photographic medium, including the reaction product of asulphurized asphalt composition and ether.

This specification signed this 10th day of December, 1926.

ALEX BROOKING DAVIS.

Patent No. 1*, 751,908.

CERTIFICATE OF CORRECTION.

ALEX nRooKmG DAVIS.

It ishereby certified that error appears in the printed specification ofthe above numbered patent requiring correction as follows: Page 5, line22, claim '30, for the word "coacting" read "coating"; and line 24, for"chloride" read "chlorine"; and that the said LettersPatent sho ild heread with these correc-. tions therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 15th day of April, 'A. D. 1930.

M. J. Moore,

(Seal) Acting Commissioner of Patents.

Granted March 25. 1930. m

